Chapter 15 Flashcards
what is corrosion caused by?
chemical reactions between the metal and the chemicals in the environment
what is rusting?
the corrosion of iron
what two conditions are needed for iron to rust?
oxygen and water
why does the mass of iron increase as it rusts?
the atoms bond with the oxygen and water molecules, which makes a compound that is heavier than iron
equation for the rusting of iron III
iron + oxygen + water -> hydrated iron (III) oxide
what happens to the iron when it rusts?
it is oxidised
3 ways of barriers to stop rusting
paint
oil/grease
plastic
what is the sacrificial method of preventing rusting?
a more reactive metal is placed onto the iron so the iron stays intact
what happens when iron is galvanised?
it is covered with a layer of zinc so the oxygen and water oxidise and react with zinc, not iron
why isn’t aluminium completely destroyed by corrosion?
aluminium oxide forms a protective layer that stops any further reactions taking place
why is iron completely destroyed by rusting?
iron oxide is flaky and will fall off to leave more iron exposed to react again
what is an alloy?
a mixture of a metal and another material
why are alloys much harder than normal metals?
the structure of the metal is disrupted so the layers can’t slide over eachother
what is bronze made from?
copper + tin
why is bronze better than copper?
it is much harder
uses of bronze 3
make medals, decorative ornaments and statues
what is brass made from?
copper + zinc
why is brass better than bronze?
it is more malleable and is used where there needs to be little friction
uses of brass 3
musical instruments, taps, door fittings
what is the most useful property of aluminium?
its low density
why is aluminium alloyed?
to make it stronger
uses of aluminium alloys 2
aircraft
plating on military vehicles
why is gold alloyed?
to make it stronger
why is copper mixed with gold?
it is more long wearing
uses of gold alloys
jewellery
what is 24 carat gold?
pure gold
how to work out how much gold is in a carat?
divide number by 24
what are steels?
alloys of iron with carbon and other elements
what are the simplest steels?
carbon steels
how are carbon steels made?
most of the carbon is removed is removed from the iron
uses of carbon steels 3
car bodies
ships
structural steel
properties of high carbon steels 2
strong but brittle
properties of low carbon steels 2
soft and easily shaped
what are nickel-steel alloys used for and why?
long-span bridges, bicycle chains
resistant to stretching forces
what is stainless steel made from?
chromium and nickel
characteristics of stainless steel? 2
don’t rust
very strong
uses of stainless steels
cutlery, cooking utensils,
what do the properties of a polymer depend on?
the monomers used to make it
the conditions under which the reaction happened
what are the two types of polyethene?
low density polyethene
high density polyethene
how is low density polyethene made?
very high temperatures and a catalyst
what is LD polyethene used for and why?
plastic bags and bottles
it is very flexible
what gives LD polyethene its low density?
the polymer chains are randomly branched and can’t pack closely together
how is HD polyethene made?
lower temperature (50c) and a different catalyst(
use of LD polyethene and why
water tanks
it is very rigid
what gives HD polyethene its high density?
the polyethene chains are straighter and can pack together more closely
what are thermosetting polymers?
they don’t soften when heated because of the ‘cross links’ between polymer chains
what are thermosoftening polymers?
they soften when heated
made of individual polymer chains tangled together
what allows thermosoftening polymers to soften under heat?
weak intermolecular forces between the polymer chains that need little energy to overcome
when it cools, the forces bring the polymer back together again
what stops thermosetting polymers from softening under heat?
the monomers form covalent ‘cross links’ between polymer chains which are strong and won’t soften
what is glass mainly made from?
sand
how is glass made?
the raw materials (sand, limestone and sodium carbonate) are heated to 1500c
they melt and react to form molten glass
when they cool, they remain in this disorganised structure
how to make different types of glass
use different raw materials
what is different about borosilicate glass and what is it used for?
it has boron trioxide in it
it is used for oven ware as it has a high melting point
what are ceramics?
non metal solids with high melting points that aren’t made from carbon based compounds
examples of ceramics made form clay 3
bricks, crockery and toilets
how are clay ceramics made?
wet clay is moulded into desired shape and heated at 1000c
why do the properties of clay change so drastically when heated?
there is ionic bonding between metals and non metals in clay
covalent bonding between non metals
arranged in giant layers
when wet, water gets between layers and makes them slimy
when they are heated, water is driven out and strong bonds form between layers
what are composites made from?
one material embedded in another
4 examples of composites
fibreglass
carbon fibre
concrete
wood
why is natural wood so strong?
cellulose
what is a matrix in a composite?
it acts as a binder and holds everything together
what is fibreglass made from?
fibres of glass embedded in a matrix made of plastic
properties of fibreglass 2
low density
very strong
what is fibreglass used for? 3
skis
boats
surfboards
what is concrete made from?
aggregate (sand and gravel) embedded in cement
use of concrete
building materials
what is carbon fibre made from?
long chains of carbon atoms in plastic
carbon nanotubes in plastic
use of carbon fibres
aerospace
sports car manufacturing
what do most fertilisers contain?
nitrogen, phosphorous and potassium
why do fertilisers contain nitrogen and similar nutrients
crops grow and absorb nutrients for growth
farmers harvest plants, so little of the plant is allowed to decompose and add nutrients back to the soil
so farmers have to replace the missing nutrients or provide more of them
even though there is a lot of nitrogen in the air, why don’t plants absorb it?
the gas is insoluble in water and plants can only absorb a soluble form of nitrogen
what is the haber process?
nitrogen and hydrogen are converted to ammonia, which is used in fertilisers
who created the haber process?
german scientist Fritz haber
what is the most important use of ammonia?
fertilisers
how is the nitrogen for the Haber process sourced?
obtained from the air
how is hydrogen sourced for the Haber process?
methane is reacted with steam to form hydrogen and carbon dioxide
what are the three conditions used in the haber process?
iron catalyst high pressure (200 atmospheres) high temperature (450c)
the Haber process:
nitrogen and methane are sourced
they are passed over an iron catalyst at high temperature and pressure
this reaction is reversible so some ammonia formed is converted back to the raw materials
a dynamic equilibrium is reached
ammonia formed as a gas
it is collected, condensed and turned into fertiliser
the unused reactants are recycled so nothing is wasted
how is ammonia obtained from the Haber process?
the gases are cooled
ammonia liquefies and can be separated
equation for haber process
nitrogen + hydrogen (half arrows) ammonia (+ heat)
N2 + 3H2 (half arrows) 2NH2 (+ heat)
equation for the formation of hydrogen
methane + steam -> hydrogen + carbon dioxide
why are fertilisers used?
replace missing nutrients
increases crop yield
crops grow faster and bigger
how to create ammonia nitrate
ammonia + nitric acid
how is ammonia phosphate formed?
ammonia + phosphoric acid
when are salts formed?
when acids and alkalis react together in a neutralisation reaction
is ammonia solution alkali or acid
alkali
how is ammonium nitrate formed in industry?
in giant vats
high concentrations
very exothermic reaction
the heat released evaporates water, leaving a very concentrated ammonium nitrate product
how is ammonium nitrate formed in the lab?
smaller scale titration and crystallisation reactants are at a lower concentration less heat produced after titration, the solution is crystallised to result in pure ammonium nitrate crystals
why is crystllisation not used in industry?
it is too slow
how to make ammonium sulfate?
react ammonia with sulfuric acid
what is NPK fertiliser?
Nitrogen, phosphorous and potassium fertiliser
where to source phosphorous?
rocks
why is acid added to phosphorous rocks?
plants can’t use it as it is insoluble in water
what is produced when phosphate rock is reacted with nitric acid?
phosphoric acid and calcium nitrate
what is produced when phosphate rock is reacted with sulfuric acid?
calcium sulfate and calcuim phosphate
also known as single superphosphate
what is produced when phosphate rock is reacted with phosphoric acid?
tripe superphosphate
how is nitrogen obtained from air?
air is cooled to -200c to liquefy it
fractional distillation happens
reaction for methane + steam
methane + steam -> hydrogen + carbon monoxide
what is the main cost of producing ammonia?
sourcing the methane, which is a natural gas
why is 200 atmospheres of pressure used?
there are less moles of ammonia than reactants
so, higher pressure = higher yield
but, higher pressure is also expensive and dangerous
so 200 atmospheres is a compromise
why is an iron catalyst used?
it speeds up both the forward and reverse reaction
doesn’t affect yield of ammonia but makes it be produced quicker
what is the forward reaction of the production of ammonia?
exothermic
why is 450c used for the Haber process?
forward reaction is exothermic
increasing temperature = less yield
but decreasing temperature = slower rate of reaction and minimises effect of catalyst
450c is a compromise between maximum yield and speed of reaction
